The invention relates to an oxidic catalyst for the conversion of water gas.
The most important and most frequently used method to produce hydrogen, for instance, for the synthesis of ammonia, is probably the conversion of water gas. Water gas, which is obtained, for instance, through gasification of coal and consists of carbon monoxide and water, is converted in accordance with the reaction (so called "conversion") EQU CO + H.sub.2 O .revreaction. H.sub.2 + CO.sub.2,
where the carbon dioxide produced can easily be washed out from the hydrogen containing gas mixture under pressure with water.
Since the conversion proceeds exothermally with a heat exchange of about 10 kcal/mol, the equilibrium must be adjusted at a temperature as low as possible, which requires the use of catalysts. In practice, the conversion is usually carried out in several stages, with a rough conversion followed by scrubbing of the CO.sub.2 being performed first in high temperature stages (400 to 600.degree. C) and then a quantitative conversion in low temperature stages (200 to 400.degree. C).
In large scale processes shaped bodies of zinc oxide and copper oxide are usually used as catalysts for the conversion. Iron oxide and chromium oxide catalysts and other combinations of these four oxides are also known. However, the stability of these catalysts, particularly the mechanical stability at high temperatures, is not too good. Although it is known in catalysts for other reactions that the stability can be increased if the catalytically active metal components are applied to a carrier material containing aluminum oxide, catalysts containing aluminum oxide are not being used at present for water gas conversion. The reason for this would seem to be that the active metal components used so far are largely blocked by the presence of aluminum oxide. In "Chemical Abstracts", vol. 80, 1974, 125 328 w, an iron oxide/chromium oxide catalyst for water gas conversion at 300 to 425.degree. C is described which contains 0 to 8% aluminum oxide. It is mentioned that an Al.sub.2 O.sub.3 content of 2% increases the thermal stability but it is noted at the same time that the activity decreases with increasing aluminum oxide content.